1. Technical Field of the Invention
This invention relates generally to portable electronic equipment and more particularly to integrated circuits used within such equipment.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radios, pagers, cellular telephones, computer memory extensions (commonly referred to as thumb drives), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer, data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
As with any integrated circuit, an integrated circuit of a multiple function handheld device includes electrostatic discharge (ESD) protection circuitry. As is known, ESD protection circuitry protects transistors coupled to input and/or output pins of the integrated circuit from electrostatic discharges when the integrated circuit is being handled, transported, etc.
One such ESD protection circuit includes a slope detector and a clamping device. The slope detector senses a slope of the power supply (VDD) that is charge up through ESD diode connected between input/output (I/O) Pins and VDD (or an ESD bus) during an ESD event on an I/O pin. When the slope detector senses an ESD event, it provides a signal to enable the clamping device (e.g., a large MOSFET or silicon controlled rectifier (SCR)). The slope detector consists of an RC (resistor/capacitor) delay circuit that should react to an ESD event (e.g., an ESD less than 100 nsec), but should not react to the normal power up of the supply voltage VDD (e.g., about 1μ Sec). If the ESD protection circuit falsely triggers due to a normal power up of the integrated circuit, it clamps the supply voltage low enough shutting off the integrated circuit.
As such, the RC delay should be long enough to sense an ESD event, which could be several hundred nano seconds in a Human Body Model type ESD event. However, with the RC delay set to cover the several hundred nano second ESD event, it may not have sufficient margin to avoid falsely triggering during a normal power up of VDD. Further, battery operated devices often experience extreme power surges induced by system level ESD/ EMI (electromagnetic interference), which may cause the ESD protection circuit to falsely trigger.
Therefore, a need exists for an ESD protection circuit that does not falsely trigger when the integrated circuit is active, especially for integrated circuits within multiple function handheld devices.